JPH0567360B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field] The present invention is directed to the production of oily substances from the sludge oil reaction product obtained by thermochemically reacting organic sludge such as surplus sludge generated from organic wastewater biological treatment equipment under high temperature and high pressure conditions. This relates to a method of separation and recovery. [Prior art and its problems] The amount of sewage sludge, which is a typical organic sludge, is approximately 50 million m ³ (moisture content: 98%) annually nationwide, and the amount is increasing year by year. Conventionally, in the treatment of sewage sludge, around 80% of it is dehydrated and then disposed of in a landfill.However, in this case, there is a problem in securing a landfill, and with the development of urbanization, the landfill is becoming more and more Securing it is becoming more difficult every year. In addition, sewage sludge can also be incinerated, and in this method, the treated product is incinerated ash whose volume is significantly reduced compared to the amount of sewage sludge that is the raw material to be treated, This is a very effective method in terms of volume reduction. However, this method has the problem that it requires a large amount of thermal energy to evaporate water in the sewage sludge, resulting in high running costs and being uneconomical. In response to this current situation, the inventors of the present invention have proposed
136299, proposed a liquefaction treatment method for sewage sludge. This method collects organic matter in sewage sludge under alkaline conditions at a reaction temperature of 250 to 350°C.
After reaction treatment under pressure equal to or higher than the saturated water vapor pressure at the reaction temperature, the obtained reaction treatment product is cooled, and the reaction treatment product is first separated into an aqueous phase and a slurry phase, and then separated. The dried slurry phase is further separated into an oily substance and a residual solid. However, in this method, it is very difficult to mechanically extract only the oily substance from the separated slurry phase, and for this purpose, extraction treatment and distillation operation are additionally required. Therefore, the overall oil conversion process is still not efficient and has many practical problems. [Problems to be solved by the invention] The present invention aims to solve the above-mentioned problems encountered in the conventional treatment of organic sludge such as sewage sludge, and to provide a method for efficiently separating and recovering oily substances from sludge oil conversion reaction products. Take it as a challenge. [Means for Solving the Invention] The present inventors have completed the present invention as a result of intensive research to solve the above problems. That is, according to the present invention, in a method for thermochemically reacting water-containing organic sludge under high temperature and high pressure conditions to obtain an oily substance from the reactant, after the reaction, the reactant is heated at 250°C or higher. Provided is a method for recovering oily substances from a sludge-oiling reaction product, characterized in that the oily substances are separated as a light liquid by density difference separation while maintaining the high temperature and high pressure state. In the present invention, the organic sludge used as the raw material to be treated includes sewage sludge discharged from ordinary sewage treatment plants, surplus sludge discharged from various organic wastewater biological treatment equipment, etc. There are no particular restrictions as long as it is sludge. However, if organic sludge contains too much moisture, it will consume a large amount of thermal energy to reach the temperature required for thermochemical reactions, so it is desirable to dehydrate the organic sludge to a moisture content of 85% or less. . To carry out the method of the present invention, organic sludge is held at high temperature and pressure to perform a thermochemical reaction, and then
At a temperature of 250° C. or higher, it is sufficient to simply perform density difference separation. In order to accelerate the reaction as necessary,
It is also possible to subject the organic sludge to alkaline conditions. In this case, alkaline substances are usually used to form alkaline conditions, examples of which include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium formate. , alkali metal compounds such as potassium formate, and alkaline earth metal compounds such as calcium oxide, calcium hydroxide, and magnesium hydroxide. The reaction treatment in the present invention is carried out at high temperature and pressure, and in this case, the reaction temperature is generally 250 to 350°C.
℃, preferably 300-320℃, and the reaction pressure is
Above the saturated water vapor pressure at the reaction temperature, for example, at 250℃, 41Kg/cm ² abs, at 300℃,
It is sufficient if it is 88Kg/cm ² abs or more. At this time, the holding time (reaction time) at the reaction temperature is 250℃,
At least 60 minutes, or at least 5 minutes at 300°C, is fine, but in order to reduce the amount of organic matter transferred to the aqueous phase,
It is desirable to carry out the reaction at as high a temperature as possible for a long time. However, increasing the reaction temperature or conducting the reaction for a long time will increase the initial cost, so the reaction temperature should be 300℃ or less.
A holding time of 60 minutes or less is appropriate. In the present invention, after the oil conversion reaction, the reactant is heated to 250°C.
At the above temperature, preferably around 300°C, density difference separation is carried out, but the method is not particularly limited as long as it is based on gravity sedimentation or centrifugal sedimentation. As typical methods, a static separation method can be used for gravity sedimentation, and a hydrocyclone or the like can be used for centrifugal sedimentation. The light liquid thus separated is obtained in a mixed state of an oily substance and an aqueous phase, and ordinary oil-water separation means are applied to separate the oily substance from this mixture. In general, separation means that utilize the density difference between the oily substance phase and the aqueous phase, such as gravity separation or centrifugal separation by standing still, or separation means that utilizes the coreless effect, etc. can be adopted. . Further, in the present invention, the pressure can be generated by using self-generated pressure due to water vapor from sewage sludge, but if necessary, it can also be pressurized using, for example, nitrogen gas, carbon dioxide gas, argon gas, etc. In the present invention, the oily substance obtained is only a low-density component of the oily substance produced in a thermochemical reaction, has a high calorific value, and has a low viscosity, so it can be used satisfactorily as a fuel oil. Next, FIG. 1 shows a flow sheet of a preferred embodiment of the present invention. In FIG. 1, 1 is a reactor preheating section, 2 is a reactor reaction section,
3 is a high temperature and high pressure separation device, 4 is a first cooler, 5 is a first pressure reduction device, 6 is a solid-liquid separation device, 7 is an incinerator,
8 is a waste heat boiler, 9 is a second cooler, 10 is a second pressure reducing device, and 11 is an oil-water separator. Organic sludge dehydrated to a moisture content of 85% or less, usually 70 to 80%, passes through line 12 to reactor preheating section 1.
will be introduced in This reactor preheating section is a heat exchange type reactor, and a heating medium is introduced from line 24 to preheat the organic sludge in the reactor. The heating medium used here is desirably the amount of heat recovered by the first cooler 4 in the latter stage. The preheated sludge is introduced into the reaction section 2 through the line 13, heated, and produces an oily substance through a thermochemical reaction. The conditions at this time are that the reaction temperature is 250 to 350°C, preferably
The reaction pressure may be 300 to 320°C as long as it is equal to or higher than the saturated water vapor pressure at the reaction temperature. The reaction time is usually 5
~180 minutes. The type of reactor employed here is preferably a scratched surface heat exchanger, but is not particularly limited. In FIG. 1, the preheating section 1 and the reaction section 2 are separated, but it is also possible to form an integrated reactor. The reactants are introduced into the high temperature and high pressure separator 3 through line 14, where they are separated into a heavy liquid (a mixture of oily substances with a density greater than that of water, residual solids and water).
and a light liquid (a mixture of oily substances and water with a density lower than that of water). The temperature during separation is 250
It is sufficient if the temperature is above ℃. The separation device here is preferably a gravity settling tank or a hydrocyclone that does not require a drive unit, but is not particularly limited. The heavy liquid is introduced into the first cooler 4 through the line 15, and is cooled to below 100°C by applying heat to the heat medium.
The heat medium passes through line 24 and heats preheating section 1 . The type of cooler is preferably a thin film falling heat exchanger, but is not particularly limited. The cooled heavy liquid passes through line 16 and is reduced in pressure to atmospheric pressure by first pressure reducing device 5, and then introduced into solid-liquid separation device 6 through line 17. Here, the heavy liquid is dehydrated to become a residue cake with a low moisture content, and is fed into the incinerator 7 via a line 19. On the other hand, the separated water is returned to the water treatment system through lines 18 and 31. In the incinerator 7, the residue cake and combustion air introduced from the line 20 are mixed and incinerated without adding auxiliary fuel. After incineration, the generated ash is discharged from the system through line 21, and high-temperature combustion exhaust gas is introduced into waste heat boiler 8 through line 22. Here, the exhaust gas imparts its retained heat to the heat medium and is dissipated into the atmosphere through the line 23. At this time, waste gas processing equipment such as dust collection and smoke cleaning may be installed as necessary. The heat medium heated by the waste heat boiler is used as a heat source for the reaction section 2. On the other hand, the light liquid separated by the high-temperature and high-pressure separator 3 is introduced into the second cooler 9 through the line 26,
After being cooled to 100° C. or lower, the pressure is reduced to atmospheric pressure via the line 27 in the second pressure reducing device 10.
Here again, it is preferable to employ a thin film falling type heat exchanger as the cooler. Thereafter, the light liquid is introduced into the oil/water separator 11 via line 28 and separated into an aqueous phase and an oily substance. As this oil/water separator, it is possible to adopt a separation means that utilizes a density difference, such as gravity separation or centrifugal separation by standing still, or a separation means that utilizes a coreless effect. The aqueous phase separated in the oil-water separator is returned to the water treatment system through lines 29 and 31. The oily material is recovered through line 30 and used as excess oil. [Effects of the Invention] As explained above, according to the present invention, sewage sludge, which was conventionally treated as industrial waste, can be treated with high calorific value (more than 8500 kcal/Kg) and low viscosity (at 50°C).
(200cP or less), it can be converted into an oily substance useful as a liquid fuel. In this case, the yield of oily substances is about 10 to 20% based on dry organic matter,
20-40 of the total amount of oily substances produced in thermochemical reactions
Corresponds to %. However, considering that more than 50% of the total oil produced is consumed for reaction, high-grade oil can be obtained as a surplus without special extraction or distillation operations. The method of the invention is a very advantageous method.
Therefore, the method for treating organic sludge into oil according to the present invention,
It can be said that this method is technically and economically very advantageous. [Example] Next, the present invention will be explained in more detail with reference to Examples. Example 1 Sewage sludge was selected as the organic sludge, and a dehydrated cake of mixed raw sludge discharged from a treatment plant using the standard activated sludge method was used in the test. This sludge was dehydrated using a belt press after adding a polymer flocculant. Its typical properties are shown in Table-1.

[Table] A high-pressure autoclave-type device was used as the experimental device. This device consists of an autoclave (inner volume: 300 ml) placed inside an electric heating furnace, and a sealed separation tube (inner volume: 1000 ml) placed separately in the autoclave. Inside the autoclave, a stirrer and a thin tube with a U-shaped tip are vertically disposed. This tubule is U
An opening at the bent tip is held at a height of a certain distance from the bottom of the autoclave, so that the contents of the autoclave above a certain level can be discharged to the outside through the thin tube. The other end of this thin tube is connected to a connecting tube led out to the outside through the lid of the autoclave, and this connecting tube is connected to a separation tube via a cooler and a valve. After pre-pressurizing the inside of the separation tube to 90Kg/cm ² G with nitrogen gas, approximately 170g of the dehydrated sludge was
A 300 ml autoclave was filled and sealed, thoroughly purged with nitrogen gas, and pressurized to 30 Kg/cm ² G. Next, stirring was started and heating was started at the same time. Immediately after the temperature inside the autoclave reached 300°C, stirring was stopped, and the contents were allowed to stand at 300°C for 120 minutes. At this time, the pressure inside the autoclave rose to 132Kg/cm ² G. Here, when the valve located between the autoclave and the separation tube is gradually opened, the upper light liquid of the product in the autoclave is pushed out through the thin tube due to the pressure difference between the autoclave and the separation tube, and the cooler The mixture was cooled and transferred to a separation tube. When about 40 g of the light liquid obtained here was allowed to stand for a day and night, it separated into an upper gray oily substance and a lower dark brown transparent aqueous phase. The heavy liquid remaining in the autoclave and the light liquid transferred to the separation tube were collected, and each was separated into three phases, an oily substance, a residual solid substance, and an aqueous phase, by a solvent extraction method using methylene chloride. The separation results shown in 2 were obtained.

[Table] As is clear from Table 2, the amount of oily substances that migrated into the separation tube was approximately 17% on a dry organic matter basis and 32% of the total produced oily substances, but both in calorific value and fluidity. This was a better result than the oily substance remaining in the liquid. Furthermore, the separation index expressed as the ratio of residual solids to oily substances (a value that indicates how much residual solids are attached to oily substances per unit weight) was 0.78 on the autoclave side, whereas , on the separation tube side, was as low as 0.09, and very good separation results were obtained, with almost no residual solid matter accompanying the light liquid on the separation tube side. Example 2 An experiment was conducted using the same sludge and oiling conditions as in Example 1. However, after reaching 300°C, that temperature was maintained for 60 minutes while stirring. Thereafter, heating was stopped, and the temperature was rapidly cooled to below 250°C using a fan, and heating was started again to control the temperature at 250°C. After the temperature stabilizes,
Stirring was stopped and the contents were allowed to stand at that temperature for 120 minutes. The subsequent operations are the same as in Example 1. The experimental results are shown in Table 3. The amount of oily substances that migrated into the separation tube was approximately 15.0% on a dry organic basis and 28.6% of the total produced oily substances, which was lower than in Example 1, but the separation index was 0.77 on the autoclave side. On the other hand, the separation tube side had a good value of about 0.1. The calorific value and fluidity were both better than the oily substance remaining in the autoclave.

[Table] Comparative Example 1 An experiment was conducted using the same sludge and oiling conditions as in Example 1. However, after reaching 300°C, that temperature was maintained for 60 minutes while stirring. Thereafter, heating was stopped, and the temperature was rapidly cooled to below 200°C using a fan, and heating was started again to control the temperature at 200°C. After the temperature stabilized, stirring was stopped and the contents were allowed to stand at that temperature for 120 minutes.
The subsequent operations are the same as in Example 1. The experimental results are shown in Table 4.

[Table] The amount of oily substances that migrated into the separation tube was approximately 14.3% on a dry organic matter basis, and 26.8% of the total produced oily substances, which was not much changed compared to Examples 1 and 2, but in terms of separation index. Since the separation temperature is as low as 200°C, the value on the separation tube side (0.25) is approaching the value on the autoclave side (0.72), and the separation of oily substances and residual solids cannot be said to be very good. Comparative Example 2 An experiment was conducted using the same sludge and oiling conditions as in the example. However, after reaching 300°C, the temperature was maintained for 60 minutes while stirring, then heating was stopped and the mixture was rapidly cooled to room temperature using a fan. After the pressure was reduced, the liquid in the autoclave was collected and allowed to stand for a day and night, whereupon it was separated into an upper dark brown transparent aqueous phase and a lower black precipitate phase. No oily substance was observed on the upper surface of the aqueous phase, and solvent extraction with methylene chloride revealed that almost all of the oily substance was contained in the lower precipitate.

[Brief explanation of the drawing]

FIG. 1 shows a flow sheet for a preferred embodiment of the invention. 1... Reactor preheating section, 2... Reactor reaction section, 3... High temperature and high pressure separation device, 4... First cooler, 5... First pressure reducing device, 6... Solid-liquid separation device,
7...Incinerator, 8...Waste heat boiler, 9...Second
Cooler, 10...second pressure reducing device, 11...oil/water separation device.

Claims (1)

[Claims] 1. A method for thermochemically reacting water-containing organic sludge under high temperature and high pressure conditions to obtain an oily substance from the resulting reactant, in which the reactant is reacted after the reaction.
A method for recovering oily substances from a sludge-oiling reaction product, which is characterized by separating oily substances as a light liquid by performing density difference separation under high temperature and high pressure conditions of 250°C or higher. 2. The method according to claim 1, wherein gravity sedimentation is performed as the density difference separation method, and the oily substance is separated as a floating phase.